Battery control system, battery pack, electronic device

ABSTRACT

A measurement unit ( 200 ) measures voltages and currents of battery cells ( 100 ). A battery control unit ( 400 ) calculates a present estimation value of a residual capacity of the battery cells ( 100 ) by integrating the currents. The voltages of the battery cells ( 100 ) are set to a reference voltage value V 1  serving as a trigger of a process of correcting the estimation value of the residual capacity and an alarm voltage value V a  which is a voltage higher than the reference voltage value. In addition, the battery control unit ( 400 ) continues discharge of all the battery cells ( 100 ), as it is, when an alarm condition in which a voltage of a minimum capacity cell is equal to or less than the alarm voltage value is not satisfied, and outputs a first signal when the voltage of the minimum capacity cell satisfies the alarm condition.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2013/000710 filed Feb. 8, 2013, claiming priority based onJapanese Patent Application No. 2012-044634, filed Feb. 29, 2012, thecontents of all of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a battery control system, a batterypack and an electronic device.

BACKGROUND ART

Various methods for using a battery pack continuously are proposed.

Patent Document 1 (Japanese Unexamined Patent Publication No.2003-217679) discloses the following discharge method. Whenever abattery voltage drops to a discharge termination voltage duringdischarge of a secondary battery, the secondary battery isintermittently discharged while repeating a temporary stop. In thiscase, when the discharge is restarted after a temporary stop, thedischarge is performed while a discharge current is reduced in astepwise manner. Thereby, compared to a case where high-rate dischargeis performed continuously, it is possible to extract a great deal ofpower from a secondary battery.

In addition, Patent Document 2 (Japanese Unexamined Patent PublicationNo. H5-87896) discloses a battery residual capacity detection andcorrection method as described below. A battery residual capacitycalculation value calculated from current consumption is corrected onthe basis of a real battery residual capacity which is obtained inadvance. Thereby, it is possible to perform a display or the like byfurther reducing a difference between a battery residual capacity and abattery residual capacity calculation value and obtaining an accuratebattery residual capacity calculation value.

RELATED DOCUMENTS Patent Documents

[Patent Document 1] Japanese Unexamined Patent Publication No.2003-217679

[Patent Document 2] Japanese Unexamined Patent Publication No. H5-87896

DISCLOSURE OF THE INVENTION

A battery pack or an electronic device using the battery pack may beprovided with a display unit that displays a present residual capacityto a user. Such a display of a residual capacity may be forciblycorrected depending on the state of the battery pack. In this manner, adrastic change in residual capacity to be displayed is inconvenient fora user.

According to the present invention, there is provided a battery controlsystem including: a measurement unit that measures voltages and currentsof a plurality of battery units which are connected in series to eachother; and a battery control unit that controls discharge of the batteryunits on the basis of the voltages measured by the measurement unit,wherein the battery control unit specifies a minimum capacity unit inwhich the voltage is lowest, on the basis of the voltages measured bythe measurement unit, when the discharge of the battery units isperformed, calculates an estimation value of a present residual capacityof the battery units by integrating the currents, sets the voltages ofthe battery unit to a reference voltage value serving as a trigger of aprocess of correcting the estimation value of the residual capacity andan alarm voltage value which is a voltage higher than the referencevoltage value, continues the discharge of all the battery units, as itis, when an alarm condition in which the voltage of the minimum capacityunit is equal to or less than the alarm voltage value is not satisfied,and outputs a first signal when the voltage of the minimum capacity unitsatisfies the alarm condition.

According to the present invention, there is provided a battery packincluding: a plurality of battery units which are connected in series toeach other; a measurement unit that measures voltages and currents ofthe battery units; and a battery control unit that controls discharge ofthe battery units on the basis of the voltages measured by themeasurement unit, wherein the battery control unit specifies a minimumcapacity unit in which the voltage is lowest, on the basis of thevoltages measured by the measurement unit, when the discharge of thebattery units is performed, calculates an estimation value of a presentresidual capacity of the battery units by integrating the currents, setsthe voltages of the battery unit to a reference voltage value serving asa trigger of a process of correcting the estimation value of theresidual capacity and an alarm voltage value which is a voltage higherthan the reference voltage value, continues the discharge of all thebattery units, as it is, when an alarm condition in which the voltage ofthe minimum capacity unit is equal to or less than the alarm voltagevalue is not satisfied, and outputs a first signal when the voltage ofthe minimum capacity unit satisfies the alarm condition.

According to the present invention, there is provided an electronicdevice including: a battery pack that includes a plurality of batteryunits which are connected in series to each other; a measurement unitthat measures voltages and currents of the battery units; a batterycontrol unit that controls discharge of the battery units on the basisof the voltages measured by the measurement unit; a load that consumespower of the discharge from the battery pack; and a load control unit,connected to the battery control unit, which controls the load, whereinthe battery control unit specifies a minimum capacity unit in which thevoltage is lowest, on the basis of the voltages measured by themeasurement unit, when the discharge of the battery units is performed,calculates an estimation value of a present residual capacity of thebattery units by integrating the currents, sets the voltages of thebattery unit to a reference voltage value serving as a trigger of aprocess of correcting the estimation value of the residual capacity andan alarm voltage value which is a voltage higher than the referencevoltage value, continues the discharge of all the battery units, as itis, when an alarm condition in which the voltage of the minimum capacityunit is equal to or less than the alarm voltage value is not satisfied,and outputs a first signal when the voltage of the minimum capacity unitsatisfies the alarm condition, and the load control unit reduces thedischarge current when the first signal is received from the batterycontrol unit.

According to the present invention, the voltages of the battery unitsare set to the reference voltage value serving as a trigger of a processof correcting the estimation value of the residual capacity and thealarm voltage value which is a voltage higher than the reference voltagevalue. When the alarm condition in which the voltage of the minimumcapacity unit is equal to or less than the alarm voltage value issatisfied, the battery control unit outputs the first signal. Theelectronic device having received the first signal reduces the dischargecurrent from the battery pack. Thereby, it is possible to prevent theestimation value of the residual capacity from being forcibly correcteddue to the voltages of the battery units reaching the reference voltagevalue, and to use the battery pack continuously.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned objects, other objects, features and advantages willbe made clearer from the preferred embodiments described below, and thefollowing accompanying drawings.

FIG. 1 is a circuit diagram illustrating a configuration of a batterypack and an electronic device according to a first embodiment.

FIG. 2 is a flow diagram illustrating a discharge control methodaccording to the first embodiment.

FIG. 3(a) shows a relationship between the time from a discharge starttime and the voltage of the minimum capacity cell in the firstembodiment. FIG. 3(b) shows a relationship between the time from thedischarge start time and the residual capacity of the minimum capacitycell in the first embodiment.

FIG. 4(a) shows a relationship between the time from the discharge starttime and the voltage of the minimum capacity cell in the comparativeexample. FIG. 4(b) shows a relationship between the time from thedischarge start time and the residual capacity of the minimum capacitycell in a comparative example.

FIG. 5 is a flow diagram illustrating a discharge control methodaccording to a second embodiment.

FIG. 6(a) shows a relationship between the time from the discharge starttime and the voltage of the minimum capacity cell in the secondembodiment. FIG. 6(b) shows a relationship between the time from thedischarge start time and the residual capacity of the minimum capacitycell in the second embodiment.

FIG. 7 is a schematic diagram illustrating a configuration of anelectronic device according to a third embodiment.

FIG. 8 is a schematic diagram illustrating a configuration an electronicdevice according to a fourth embodiment.

FIG. 9 is a schematic diagram illustrating a configuration of anelectronic device according to a fifth embodiment.

FIG. 10 is a circuit diagram illustrating a configuration a battery packand an electronic device according to a sixth embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings. In all the drawings, likeelements are referenced by like reference numerals and descriptionsthereof will not be repeated.

The term “battery pack 10” as used herein refers to an assembled batteryhaving a plurality of battery units. In addition, the term “batteryunit” refers to a unit having at least one or more battery cells 100.Further, the battery cell 100 included in the “battery unit” may includea plurality of single batteries having a positive electrode, a negativeelectrode and the like. In addition, a plurality of “battery units” mayinclude a different quantity of the battery cells 100, respectively. Inthe following, a description will be given of a case where the “batteryunit” included in the “battery pack 10” is the battery cell 100 havingtwo single batteries which are connected in parallel to each other.

First Embodiment

The battery pack 10 according to the first embodiment will be describedwith reference to FIG. 1. FIG. 1 is a circuit diagram illustrating aconfiguration of the battery pack 10 and an electronic device 60according to the first embodiment. The battery pack 10 includes aplurality of battery cells 100, a measurement unit (measurement unit200), and a battery control unit (battery control unit 400). Theplurality of battery cells 100 are connected in series to each other.The measurement unit 200 measures the voltages and currents of thebattery cells 100. The battery control unit 400 controls discharge ofthe battery cells 100 on the basis of the voltages measured by themeasurement unit 200. When the discharge of the battery cells 100 isperformed, the battery control unit 400 specifies a minimum capacitycell having the lowest voltage on the basis of the voltages measured bythe measurement unit 200. In addition, the battery control unit 400calculates an estimation value of the residual capacity of the presentbattery cell 100 by integrating a current. A reference voltage value V₁serving as a trigger of a process of correcting the estimation value ofthe residual capacity and an alarm voltage value V_(a) which is avoltage higher than the reference voltage value are set as the voltagesof the battery cells 100. In addition, the battery control unit 400continues the discharge of all the battery cells 100, as it is, when analarm condition in which the voltage of the minimum capacity cell isequal to or less than the alarm voltage value is not satisfied, andoutputs a first signal when the voltage of the minimum capacity cellsatisfies the alarm condition. Hereinafter, a detailed description willbe given.

As shown in FIG. 1, the battery pack 10 includes a plurality of batterycells 100. Here, the battery pack 10 includes, for example, N batterycells 100. In addition, as described above, the battery cell 100 has twosingle batteries. Specifically, the battery cell 100 is a Li-ionsecondary battery. In addition, the battery cell 100 is, for example, alaminate-type battery in which a laminate film is used in an exteriormaterial. In the battery pack 10 according to the first embodiment, theplurality of battery cells 100 are received in exterior bodies (notshown), respectively, and are packaged in the battery pack 10 in a statewhere the battery cells are placed in a row. Meanwhile, the packageaspect of the battery cell 100 may be formed in an arbitrary manner, andmay be formed, for example, in a state where the plurality of batterycells 100 are laminated in a row in the thickness direction thereof, orin a state where the laminated battery cells 100 are disposed adjacentto a plurality of rows. In such a package or the like, it is alsopossible to obtain the same effect as that in the first embodiment.

The full charge capacity of the battery pack 10 is reduced by repeatingcharge and discharge. In this process, it is not always true that thefull charge capacity of each of the battery cells 100 is reducedequally. When the battery pack 10 is discharged, the battery cell 100 ofwhich the full charge capacity is most reduced has a drop in voltageduring discharge faster than other battery cells 100. The “full chargecapacity” as used herein refers to a capacity (having a unit of Ah) whenthe battery cell 100 is fully charged. Here, the battery cell 100 havings smallest full charge capacity is called the “minimum capacity cell”.

The battery pack 10 according to the first embodiment includes a controlcircuit 20 in addition to the battery cells 100. The control circuit 20includes a measurement unit 200, a battery control unit 400 and a switch500.

In addition, the control circuit 20 is connected to the battery cells100 which are connected in series to each other. The control circuit 20includes an internal positive electrode terminal 160, an internalnegative electrode terminal 180, an external positive electrode terminal710 and an external negative electrode terminal 720. The internalpositive electrode terminal 160 is connected to a positive electrodeterminal 120 of one battery cell 100 connected in series. In addition,the internal negative electrode terminal 180 is connected to a negativeelectrode terminal 140 of the other battery cell 100 connected inseries.

The internal positive electrode terminal 160 is connected to theexternal positive electrode terminal 710 for connection to an externaldevice using the battery pack 10 through an interconnect (not shown)within the control circuit 20. In addition, the internal negativeelectrode terminal 180 is also connected to the external negativeelectrode terminal 720 similarly.

The switch 500 for stopping charge or discharge is provided between theinternal positive electrode terminal 160 and the external positiveelectrode terminal 710. The switch 500 is provided between, for example,the internal positive electrode terminal 160 on the battery cell 100side and the external positive electrode terminal 710. In this case, theswitch 500 is, for example, a P-channel metal oxide semiconductor fieldeffect transistor (MOSFET). Two P-channel MOSFETs are provided withinthe switch 500. Thereby, one MOSFET is used for controlling charge. Onthe other hand, the other MOSFET is used for controlling discharge. Inaddition, each MOSFET in the switch 500 is connected to the measurementunit 200.

Meanwhile, when the switch 500 is an N-channel MOSFET, the switch 500 isdisposed between the internal negative electrode terminal 180 and theexternal negative electrode terminal 720. Besides, the switch 500 maybe, for example, an insulated gate bipolar transistor (IGBT), a relay ora breaker.

The measurement unit 200 measures the voltage and current of theplurality of battery cells 100. The measurement unit 200 is connectedbetween the battery cells 100 through an interconnect (no sign shown).In addition, the measurement unit 200 measures a voltage of both ends ofthe internal positive electrode terminal 160 and internal negativeelectrode terminal 180 in order to measure the total voltage of theplurality of battery cells 100 which are connected in series to eachother.

In addition, a resistor 220 of which the resistance value is known isprovided between the internal negative electrode terminal 180 and theexternal negative electrode terminal 720. The measurement unit 200 isconnected to both ends of the resistor 220. In this manner, by measuringa voltage value applied to the resistor 220, the measurement unit 200calculates a value divided by the above resistance value as a value of acurrent flowing through the battery cell 100.

The battery control unit 400 is connected to the measurement unit 200.The battery control unit 400 controls the discharge of the battery cells100 on the basis of the voltages measured by the measurement unit 200.The battery control unit 400 includes an arithmetic operation unit (notshown) that performs an arithmetic operation process on the basis of thevoltages of the battery cells 100 measured by the measurement unit 200.For example, when the discharge of the battery cells 100 is performed,the battery control unit 400 specifies the minimum capacity cell havingthe lowest voltage on the basis of the voltages measured by themeasurement unit 200.

The battery control unit 400 includes a communication unit (not shown)for transmitting various types of signals to the electronic device 60 orreceiving a signal from the electronic device 60. The battery controlunit 400 is connected to a communication terminal 730 for transmittingand receiving a signal to the electronic device 60.

In addition, the arithmetic operation unit of the battery control unit400 calculates a current value from a voltage value of both ends of aresistor 220 which is measured by the measurement unit 200. The batterycontrol unit 400 calculates an estimation value of the residual capacityof the present battery cell 100 by integrating the current value. The“estimation value of the residual capacity” of the battery pack 10 is atotal residual capacity of all the battery cells 100 which has beenintegrated since the charge.

This “estimation value of the residual capacity” is used, for example,for causing a user to recognize the residual capacity. Specifically, thebattery control unit 400 outputs a residual capacity signal indicatingthe estimation value of the residual capacity of the battery cell 100.The signal is transmitted to a load control unit 640 of the electronicdevice 60 through the communication terminal 730. Thereby, for example,it is possible to notify a user of the estimation value of the residualcapacity through a display unit of the electronic device 60 or the like.

Meanwhile, the battery pack 10 may include a display unit (not shown)that displays the estimation value of the residual capacity of thebattery cell 100. Thereby, even when which electronic device 60 is used,it is possible to cause a user to recognize the estimation value of theresidual capacity of the battery cell 100.

In addition, the battery control unit 400 includes a storage unit (notshown) that stores the measured voltage and current or various types ofsettings. The storage unit refers to, in other words, a memory region.The reference voltage value V₁ and the alarm voltage value V_(a)described later are set as the voltages of the battery cells 100. Thereference voltage value V′, the alarm voltage value V_(a), theestimation value of the residual capacity, and the like are stored inthe storage unit of the battery control unit 400.

The “reference voltage value V₁” as used herein refers to a voltagevalue serving as a trigger of a process of correcting the estimationvalue of the residual capacity. When the voltage of the minimum capacitycell becomes the reference voltage value V′, the battery control unit400 forcibly corrects the estimation value of the residual capacitycalculated by the battery control unit 400 to a predetermined “firstvalue” (for example, 10% of the full charge capacity as describedlater), regardless of the estimation value. That is, the battery controlunit 400 forcibly corrects the estimation value of the residual capacityto the predetermined first value due to a drop in the voltage of theminimum capacity cell even in a state where the residual capacities ofother battery cells 100 remain.

In addition, the “reference voltage value V₁” is higher than a dischargetermination voltage value V₀ at which the battery cell 100 isover-discharged. Thereby, it is possible to inform a user of a drop inresidual capacity before the minimum capacity cell is over-discharged.

For example, a user recognizes the residual capacity of the battery pack10 on the basis of a display residual capacity of the display unit ofthe battery pack 10 or the electronic device 60, and uses the electronicdevice 60. Here, when the voltage of the minimum capacity cell drops tothe reference voltage value V₁, the battery control unit 400 correctsthe estimation value of the residual capacity to the first value andoutputs a signal. For example, the load control unit 640 of theelectronic device 60 having received the signal performs a display suchas “the residual capacity of the battery cell 100 drops to the firstvalue” on the display unit or the like. Thereby, it is possible toindirectly inform a user that the voltage of the minimum capacity celldrops.

Meanwhile, the “first value” to which the residual capacity is forciblycorrected refers to a value larger than at least 0 which is set inadvance. Specifically, for example, the “first value” is set bymeasuring a standard (average) battery cell 100 in advance, and is avalue of the residual capacity when the voltage of the standard batterycell 100 becomes the reference voltage value V₁ in a case where thestandard battery cell 100 is discharged at a predetermined constantcurrent. Alternatively, the “first value” can be set to, for example, aminimum residual capacity required for shutting down the electronicdevice (60) used by a user. Meanwhile, the unit of the “first value” isAh. In addition, specifically, the “first value” of the residualcapacity is, for example, 10% of the full charge capacity. Thereby, forexample, when the electronic device 60 is a computer or the like and hasa storage unit, it is possible to prevent the device from being shutdown in a state where data cannot be stored. The “first value” is alsostored in the storage unit of the battery control unit 400.

Meanwhile, when the voltage of the minimum capacity cell becomes thereference voltage V′, and the estimation value of the residual capacitycalculated by the battery control unit 400 is equal to or less than the“first value”, the estimation value of the residual capacity is a valueclose to a real residual capacity. For this reason, the estimation valueof the residual capacity is not necessarily corrected to the “firstvalue”.

In addition, the “alarm voltage value V_(a)” as used herein is a voltagevalue for giving an alarm that the voltage of the minimum capacity cellcomes close to the voltage (reference voltage value V₁) for forciblycorrecting the estimation value of the residual capacity. For thisreason, the “alarm voltage value V_(a)” is set to a voltage value higherthan the above-mentioned reference voltage value V₁. The “alarm voltagevalue V_(a)” can be obtained by adding the measurement accuracy of themeasurement unit 200 to the reference voltage value V₁. The “measurementaccuracy of the measurement unit 200” as used herein refers to, forexample, the voltage detection accuracy of an IC of the measurement unit200. Specifically, the “alarm voltage value V_(a)” is, for example,V₁+100 mV.

The battery control unit 400 continues the discharge of all the batterycells 100, as it is, when the alarm condition in which the voltage ofthe minimum capacity cell becomes equal to or less than the alarmvoltage value is not satisfied, and outputs the first signal when thevoltage of the minimum capacity cell satisfies the alarm condition. Theelectronic device 60 having received the first signal reduces adischarge current of the battery pack 10. Thereby, it is possible toprevent the estimation value of the residual capacity from beingforcibly corrected to the first value due to the voltage of the batteryunit reaching the reference voltage value V₁. The details of thisdischarge control method will be described later.

In addition, the measurement unit 200, the battery control unit 400 andthe switch 500 improve safety and the cycle life of charge anddischarge, and thus function as protection circuits. When the batterycell 100 is discharged down to equal to or less than an over-dischargedetection voltage value lower than the discharge termination voltagevalue V₀, the measurement unit 200, the battery control unit 400 and theswitch 500 terminate the discharge forcibly.

In this manner, in the first embodiment, the battery pack 10 includingthe plurality of battery cells 100 and control circuit 20 is packaged.

Next, the electronic device 60 connected to the battery pack 10according to the first embodiment will be described. The electronicdevice 60 includes a load 600 and a load control unit (load control unit640). The load 600 of the electronic device 60 consumes power due todischarge from the battery pack 10. The load control unit 640 isconnected to the battery control unit 400, and receives a first signaland controls the load 600. In addition, when the first signal isreceived from the battery control unit 400, the load control unit 640reduces a discharge current. Hereinafter, a detailed description will begiven.

FIG. 1 schematically shows the electronic device 60. The load 600,provided therein, consumes power due to the discharge from the batterypack 10. In FIG. 1, the load 600 is shown collectively as a variableresistor that consumes power.

Here, the electronic device 60 is, for example, a display device.Specifically, the electronic device 60 is a liquid crystal displaydevice. Therefore, the electronic device 60 includes a display unit, alight-emitting unit, a tuner unit, an operating unit and the like (allnot shown) as the load 600. The load 600 includes at least one or morelight-emitting units (not shown). The light-emitting unit is, forexample, a backlight of a liquid crystal display device.

The load 600 is connected to a positive electrode terminal 810 and anegative electrode terminal 820 through an interconnect (not shown). Thepositive electrode terminal 810 and the negative electrode terminal 820of the electronic device 60 are connected to the external positiveelectrode terminal 710 and the external negative electrode terminal 720of the battery pack 10 through, for example, an interconnect (no signshown). Thereby, the electronic device 60 can receive power due to thedischarge of the battery pack 10.

The load control unit 640 is connected to the load 600. The load controlunit 640 controls the load 600. Thereby, the load control unit 640controls the amount of power consumption due to the load 600.Specifically, for example, when the load 600 includes a backlight, theload control unit 640 controls the luminance of the backlight.

In addition, the load control unit 640 is connected to a communicationterminal 830. The communication terminal 830 on the electronic device 60side is connected to the communication terminal 730 on the battery pack10 side through, for example, an interconnect (not shown). Thereby, theload control unit 640 is connected to the battery control unit 400, andcan receive the residual capacity signal and the first signal.

The electronic device 60 of the first embodiment is a display device.Therefore, the load control unit 640 can cause the display unit toreceive the residual capacity signal of the estimation value of theresidual capacity transmitted from the battery control unit 400 anddisplay the estimation value of the residual capacity.

Besides, the load control unit 640 may include an arithmetic operationunit (not shown). The arithmetic operation unit performs an arithmeticoperation process in accordance with the first signal described later,and can perform the most appropriate control on the load 600 at thatpoint in time.

When the first signal is received from the battery control unit 400, theload control unit 640 reduces a discharge current. In this case, forexample, when the load 600 includes a backlight, the load control unit640 reduces the discharge current by lowering the luminance of thelight-emitting unit. Thereby, it is possible to prevent the minimumcapacity cell from being over-discharged. In addition, it is possible toprevent the estimation value of the residual capacity from beingcorrected forcibly. The details of this discharge control method will bedescribed later.

In addition, when the first signal is received from the battery controlunit 400, the load control unit 640 may cause the display unit (notshown) of the electronic device 60 to display the start of control forreducing the discharge current. Thereby, it is possible to prepare auser for the use of the electronic device 60 being restricted.

Next, the discharge control method of the battery pack 10 stated abovewill be described with reference to FIGS. 2 and 3. FIG. 2 is a flowdiagram illustrating a discharge control method according to the firstembodiment. FIG. 3 is a diagram illustrating a discharge control methodaccording to the first embodiment. The discharge method according to thefirst embodiment includes the following steps. First, when the dischargeof the battery cells 100 is performed, a minimum capacity cell in whichthe voltage is lowest is specified on the basis of the voltages measuredby the measurement unit 200 (S120). Next, when the alarm condition inwhich the voltage of the minimum capacity cell is equal to or less thanthe alarm voltage value is satisfied (S130; Yes), the first signal isoutput (S140). Hereinafter, a detailed description will be given.

Here, each of the battery cells 100 is set to be in a state of beingcharged up to full charge. That is, the discharge voltage of each of thebattery cells 100 in an initial step is a voltage value V_(c) of fullcharge. In addition, the residual capacity of each of the battery cells100 is a full charge capacity.

First, in FIG. 2, the positive electrode terminal 810 and the negativeelectrode terminal 820 of the electronic device 60 are connected to theexternal positive electrode terminal 710 and external negative electrodeterminal 720 of the battery pack 10, respectively. Thereby, dischargefrom the plurality of battery cells 100 is started. At the same time,the measurement unit 200 measures the voltages and currents of theplurality of battery cells 100 which are connected in series to eachother (S110).

Here, power due to the discharge of the battery pack 10 is consumed bythe load 600 of the electronic device 60. In addition, the load 600 iscontrolled by the load control unit 640, and thus operates at a constantcurrent. Meanwhile, here, the internal resistance of the switch 500 isconsidered to be small enough to be negligible.

Next, the battery control unit 400 specifies the minimum capacity cellin which the voltage is lowest on the basis of the voltages measured bythe measurement unit 200 (S120).

Here, FIG. 3(a) shows a relationship between the time from a dischargestart time and the voltage of the minimum capacity cell in the firstembodiment. Solid lines show a case in which the discharge controlmethod in the first embodiment is applied. On the other hand, dottedlines show a case in which the discharge control method is not applied.

All the battery cells 100 inclusive of the minimum capacity cell areconnected in series to each other. For this reason, currents flowingthrough the respective battery cells 100 are all equal to each other.Therefore, since a full charge capacity C_(Ra) of the minimum capacitycell out of the plurality of battery cells 100 is small, a drop involtage is faster than those of other battery cells 100. Therefore, the“minimum capacity cell” is specified as the battery cell 100 having thelowest voltage. Meanwhile, in the first embodiment, since two singlebatteries are connected in parallel to each other within the batterycell 100, a large current flows through the single battery having asmaller internal resistance.

In addition, FIG. 3 (b) shows a relationship between the time from thedischarge start time and the residual capacity of the minimum capacitycell in the first embodiment, and a relationship between the time fromthe discharge start time and the current of the minimum capacity cell.Meanwhile, the residual capacity in FIG. 3(b) refers to the estimationvalue of the residual capacity calculated by the battery control unit400.

In FIG. 3(b), the load 600 is operated at a constant current by the loadcontrol unit 640. For this reason, discharge to time t₁ is constantcurrent discharge. Therefore, the discharge currents of all the batterycells 100 are a constant current value I_(D1) and are constant. Inaddition, the residual capacity of each of the battery cells 100 dropslinearly.

Meanwhile, in the initial step of the discharge, the minimum capacitycell may not be the battery cell 100 having the lowest voltage. In thatcase, the battery cell 100 having the lowest voltage may be specified asa “minimum capacity cell”, and the specified “minimum capacity cell” maybe corrected on the basis of the voltages measured at any time.

Next, the battery control unit 400 determines the alarm condition inwhich the voltage of the minimum capacity cell becomes equal to or lessthan the alarm voltage value V_(a) (S130). As described above, the“alarm voltage value V_(a)” is a voltage value for giving an alarm thatthe above voltage comes close to a voltage for forcibly correcting theestimation value of the residual capacity. Meanwhile, the “dischargereference voltage value V₁” is stored in the storage unit of the batterycontrol unit 400.

Next, when the voltage of the minimum capacity cell is higher than thealarm voltage value V_(a), and the alarm condition is not satisfied(S130; No), the battery control unit 400 continues the discharge of allthe battery cells 100 as it is.

On the other hand, when the voltage of the minimum capacity cell becomesthe alarm voltage value V_(a), and the alarm condition is satisfied(S130; Yes), the battery control unit 400 outputs the first signal forreducing the discharge current in the discharge (S140). The first signalis transmitted to the load control unit 640 of the electronic device 60through the communication terminal 730 of the battery pack 10 and thecommunication terminal 830 of the electronic device 60.

The “first signal” as used herein refers to a signal which is output inorder for the battery control unit 400 to reduce a discharge current onthe load 600 side. The “first signal” can be changed depending on theconnected electronic device 60. Specifically, the “first signal” may be,for example, a 1-bit signal for switching between the turn-on orturn-off of the load 600. In addition, the “first signal” may be, forexample, a signal corresponding to the present voltage value of theminimum capacity cell. In addition, the “first signal” may include asignal corresponding to the present current value (that is, currentvalue of the discharge current) of the battery pack 10.

In addition, a period in which the “first signal” is output can be setto only a moment when the above alarm condition is established. In thiscase, after the load control unit 640 receives the first signal, theload control unit 640 performs all the controls for reducing a dischargecurrent. On the other hand, the period in which the “first signal” isoutput may be set to a period continuing while the above alarm conditionis satisfied. In this case, the “first signal” can be changed dependingon the situation at any time. For example, the battery control unit 400can continue to transmit a signal corresponding to the present voltagevalue of the minimum capacity cell stated above.

Here, in FIGS. 3(a) and 3(b), the time when the alarm condition issatisfied (S130; Yes) is time t₁. As shown in FIG. 3(a), the voltage ofthe minimum capacity cell becomes the alarm voltage value V_(a).Therefore, the voltage of the minimum capacity cell is in a state wherethe alarm condition is satisfied. Meanwhile, although not shown in thedrawing, at time t₁, the voltages of other battery cells 100 are equalto or greater than the alarm voltage value V_(a).

In addition, as shown in FIG. 3(b), at time t₁, the residual capacity ofthe minimum capacity cell is C_(a). The residual capacity of the minimumcapacity cell in this case is larger than a first value C₁ which is acorrection value. Meanwhile, the residual capacities of all the batterycells 100 are also larger than the first value C₁ which is a correctionvalue.

Next, when the first signal is received from the battery control unit400 after time t₁, the load control unit 640 reduces the dischargecurrent (S150).

In the first embodiment, the load 600 includes a light-emitting unitsuch as a backlight. In this case, the load control unit 640 reduces thedischarge current by lowering the luminance of the light-emitting unit.

As shown in FIG. 3(b), after time t₁, the load control unit 640 reducesthe discharge current from the constant t₁, the load control unit 640can perform control so that the voltage of the minimum capacity cell hasa value larger than the reference voltage V₁, on the basis of the firstsignal. Here, the load control unit 640 reduces the discharge currentlinearly. Specifically, when the current flowing through thelight-emitting unit is reduced, the load control unit 640 drops theluminance. In this case, the residual capacity of the minimum capacitycell drops gently after time t₁.

In addition, as shown in FIG. 3(a), when the discharge current is notreduced by the load control unit 640, there is the possibility of thevoltage of the minimum capacity cell reaching the reference voltage V₁for forcibly correcting the estimation value of the residual capacity attime t₂. On the other hand, in the first embodiment, the load controlunit 640 reduces the discharge current in S150. Thereby, from time t₁ totime t₃, the voltage of the minimum capacity cell can be maintainedhigher than the reference voltage V′. Therefore, it is possible toprevent the estimation value of the residual capacity from beingforcibly corrected to the first value.

In S150, as described above, the load control unit 640 may cause thedisplay unit (not shown) of the electronic device 60 to display thestart of control for reducing the discharge current. Thereby, it ispossible to prepare a user for the use of the electronic device 60 beingrestricted.

In addition, in S150, the load control unit 640 may perform control sothat the discharge current is set to be equal to or greater than aminimum current value required for bringing the electronic device 60into operation. Thereby, it is possible to use the electronic device 60for a long time.

As shown in FIG. 3(b), further, the load control unit 640 performs thecontrol of the discharge current, and thus the residual capacity of theminimum capacity cell becomes equal to the first value C₁ which is acorrection value at time t₄.

In this case, as shown in FIG. 3(a), the voltage of the minimum capacitycell is equal to or greater than the reference value V₁ for performingcorrection. In this manner, the load control unit 640 reduces thedischarge current, and thus the voltage of the minimum capacity cellbecomes equal to or less than the reference voltage V₁. Therefore, it ispossible to prevent the estimation value of the residual capacity beingforcibly corrected. Therefore, the battery pack 10 can be usedcontinuously.

Meanwhile, it is also considered that before the residual capacity ofthe minimum capacity cell becomes equal to the first value C₁ which is acorrection value, the voltage of the minimum capacity cell becomes equalto or less than the reference voltage V₁ for performing correction. Inthis case, when the voltage of the minimum capacity cell becomes equalto or less than the reference voltage, the estimation value of theresidual capacity is corrected to the first value C₁. Herein, adifference between the estimation value of the immediately precedingresidual capacity and the first value C₁ of the correction value can bereduced by the control of the discharge current performed by theabove-mentioned load control unit 640. Therefore, it is less likely togive a user an impression of a change in residual capacity.

The load control unit 640 reduces the discharge current until thecurrent reaches 0. In this case, the battery control unit 400 terminatesthe discharge (S190).

On the other hand, the user side may terminate the use of the electronicdevice 60 arbitrarily (S190).

As described above, the discharge of the battery pack 10 according tothe first embodiment is controlled.

Next, an effect of the first embodiment will be described.

First, the need to correct the estimation value of the residual capacityof the battery cell 100 which is calculated by the battery control unit400 will be described.

As a first reason for correcting the estimation value of the residualcapacity, self-discharge of the battery cells 100 is considered. Theresidual capacity of the battery cell 100 is reduced gradually with thelapse of time in spite of the battery cell 100 not being used. When thebattery cell 100 is left unused, the residual capacity may run out.Therefore, even when the battery control unit 400 stores the estimationvalue of the residual capacity by integrating a charge current valueduring the charge of the battery pack 10, there is the possibility of areal residual capacity being lower than the estimation value of theresidual capacity during a real use of the battery pack.

As a second reason, a case is considered in which the discharge currentconsumed by the electronic device 60 is large. The battery cell 100 hasan internal resistance. For this reason, the voltage of the battery cell100 during the discharge becomes a value obtained by subtracting acomponent caused by a voltage drop due to the internal resistance. Whenthe discharge current is large, the contribution of the voltage drop dueto the internal resistance increases. For this reason, particularly, thevoltage of the minimum capacity cell drops drastically, and thus thereis the possibility of over-discharge occurring. Therefore, the referencevoltage V₁ for forcibly correcting the estimation value of the residualcapacity is set, and the over-discharge of the battery cells 100 isprevented beforehand from occurring.

From such reasons, it is necessary to correct the estimation value ofthe residual capacity of the battery cell 100 which is calculated by thebattery control unit 400.

Next, the effect of the first embodiment will be described using FIG. 4as a comparative example. FIG. 4 is a diagram illustrating a comparativeexample for describing the effect of the first embodiment.

Unlike the first embodiment, FIG. 4 shows a comparative example in whichthe battery control unit 400 does not perform control of the dischargeof the minimum capacity cell. FIG. 4(a) shows a relationship between thetime from the discharge start time and the voltage of the minimumcapacity cell in the comparative example. In addition, FIG. 4(b) shows arelationship between the time from the discharge start time and theresidual capacity of the minimum capacity cell in the comparativeexample, and a relationship between the time from the discharge starttime and the current of the minimum capacity cell. Meanwhile, time t ofFIG. 4 is assumed to be the same as time t of FIG. 3. In addition, thedischarge current is assumed to be the constant current value I_(D1) andbe constant.

As shown in FIG. 4(a), in the comparative example, the voltage of theminimum capacity cell id reduced monotonically from the discharge start.Here, the voltage of the battery cell 100 drops even due to the internalresistance of the battery cell 100, in addition to a drop due to thedischarge of the battery cells 100. A voltage drop component due to theinternal resistance of the battery cell 100 is proportional to thedischarge current. In addition, the internal resistance of the minimumcapacity cell of which the full charge capacity is most reduced islarger than those of other battery cells 10. Therefore, a voltage dropcomponent due to the internal resistance of the minimum capacity cell islarger than voltage drop components of the internal resistances of otherbattery cells 100. Thus, a drop in the voltage of the minimum capacitycell is faster than those of other battery cells 100.

In the comparative example, a case does not occur in which the batterycontrol unit 400 outputs the first signal as in the first embodiment. Inaddition, the load control unit 640 does not perform the control forreducing the discharge current. Therefore, the voltage of the minimumcapacity cell continues to drop along with a reduction in residualcapacity even when the voltage becomes lower than the alarm voltagevalue V_(a).

At time t₂, the voltage of the minimum capacity cell further drops tothe reference voltage V₁ for correcting the estimation value of theresidual capacity. In this manner, the voltage of the minimum capacitycell reaches the reference voltage V₁ faster than those of other batterycells 100. In this case, when the voltage of the minimum capacity celldrops to the reference voltage V₁, the battery control unit 400 forciblycorrects the estimation value of the residual capacity to the firstvalue C₁ which is a correction value. Further, the battery control unit400 transmits the corrected estimation value of the residual capacity tothe load control unit 640 of the electronic device 60 through thecommunication terminal 730.

In addition, as shown in FIG. 4(b), the residual capacity of the minimumcapacity cell is reduced linearly. At time t₂, as described above, thevoltage of the minimum capacity cell drops to the reference voltage V₁by the contribution of the voltage drop due to the internal resistance.For this reason, the residual capacity of the minimum capacity cell isequal to or greater than the first value C₁ which is a correction value,but is forcibly corrected to the first value C₁.

In addition, at a point in time t₂, the residual capacities of otherbattery cells 100 are also equal to or greater than the first value C₁.Therefore, in the comparative example, there is the possibility of theresidual capacities being corrected to the first value C₁ in a statewhere a large amount of residual capacity remains, in a whole of thebattery pack 10.

In this manner, when the estimation value of the residual capacity iscorrected, a user receives a feeling such as a reduction in residualcapacity. For this reason, in the first embodiment, the forciblecorrection of the estimation value of the residual capacity issuppressed as follows.

According to the first embodiment, the alarm voltage value V_(a) whichis a voltage higher than the reference voltage value V₁ is set as thevoltages of the battery units in addition to the reference voltage valueV₁ serving as a trigger of a process of correcting the estimation valueof the residual capacity to the first value lower than a valuecalculated by the battery control unit. When the alarm condition inwhich the voltage of the minimum capacity unit is equal to or less thanthe alarm voltage value V_(a) is satisfied, the battery control unitoutputs the first signal. Thereby, it is possible to reduce thedischarge current with respect to the electronic device 60, connected tothe battery pack 10, which has received the first signal.

In addition, for example, when the discharge current consumed in theload 600 is reduced by the load control unit 640 of the electronicdevice 60, the consumption of the residual capacity of the minimumcapacity cell is reduced. In addition, the above-mentioned voltage dropdue to the internal resistance of the battery cell 100 is reduced.Thereby, it is possible to delay the voltage of the minimum capacitycell reaching the reference voltage value V₁ for correcting theestimation value of the residual capacity. Therefore, it is possible toprevent the estimation value of the residual capacity from beingforcibly corrected due to the voltage of the minimum capacity cellreaching the reference voltage value V₁. In other words, it is possibleto perform control so that the behavior of the voltage drop of theminimum capacity cell corresponds to the real residual capacity.

As described above, according to the first embodiment, it is possible toprevent the estimation value of the residual capacity from beingforcibly corrected due to the voltage of the minimum capacity cellreaching the reference voltage value V₁, and to use the battery packcontinuously.

Modified Example

As described above, in the first embodiment, a case where the electronicdevice 60 is a liquid crystal display device has been described, but theelectronic device may be a display device including a plurality oflight-emitting units such as an organic EL element as pixels. In thiscase, when the load control unit 640 receives the first signal, it ispossible to reduce, for example, a current flowing through all thelight-emitting units.

In addition, in the first embodiment, a case has been described in whichthe voltage of the minimum capacity cell is equal to or greater than thereference voltage V₁ when the residual capacity of the minimum capacitycell becomes equal to the first value C₁ which is a correction value, bythe above-mentioned control. However, it is also considered that beforethe voltage of the minimum capacity cell becomes the reference voltageV₁, the estimation value of the residual capacity calculated by thebattery control unit 400 becomes the “first value”. In this case, theestimation value of the residual capacity is a value smaller than thereal residual capacity. In this case, the battery control unit 400 mayperform control as follows.

The battery control unit 400 performs a correction for maintaining theestimation value of the residual capacity to be the “first value” untilthe estimation value of the residual capacity becomes the “first valueC₁” and then the voltage of the minimum capacity cell becomes thereference voltage V₁. Next, the battery control unit 400 stops thiscorrection using the setting of the voltage of the minimum capacity cellto the reference voltage V₁ as a trigger. Thereafter, the batterycontrol unit 400 may calculate the estimation value of the residualcapacity again from the “first value C₁”. In this manner, the estimationvalue of the residual capacity can be brought closer to the realresidual capacity.

Meanwhile, in the above-mentioned first embodiment, the “estimationvalue of the residual capacity” has set to a total residual capacity ofall the battery cells 100 which has been integrated since the charge.However, the “estimation value of the residual capacity” is not limitedthereto. It is also possible to obtain the same effect as that in thefirst embodiment, for example, using a capacity obtained by adding andsubtracting (subtraction in discharge and addition in charge) thecumulative integration amount of a charge and discharge current from thefull charge capacity of the battery pack 10 which is measured inadvance.

In this case, the full charge capacity of the battery pack 10 isobtained by measuring the time integration value of the charge currentduring the charge of the battery pack 10 without interposing thedischarge between the discharge termination voltage and the full charge.Meanwhile, constant-current constant-voltage charge is performed on thebattery pack 10 in a case of the full charge, and the above capacity isobtained when the charge current becomes equal to or less than thereference value which is set in advance. In addition, the timeintegrated value of the current may be measured as electric quantity(coulomb) using a coulomb counter or the like.

Second Embodiment

A second embodiment will be described with reference to FIGS. 5 and 6.FIG. 5 is a flow diagram illustrating a discharge control methodaccording to the second embodiment. FIG. 6 is a diagram illustrating adischarge control method according to the second embodiment. The secondembodiment is the same as the first embodiment, except that the contentsof control performed by the load control unit 640 after S150 aredifferent. Hereinafter, a detailed description will be given.

The same battery pack 10 can be used in the second embodiment as in thefirst embodiment. In addition, the electronic device 60 is, for example,a display device as is the case with the first embodiment.

FIG. 6(a) shows a relationship between the time from the discharge starttime and the voltage of the minimum capacity cell in the secondembodiment. In addition, FIG. 6 (b) shows a relationship between thetime from the discharge start time and the residual capacity of theminimum capacity cell in the second embodiment, and a relationshipbetween the time from the discharge start time and the current of theminimum capacity cell.

Here, as shown in FIG. 6(a), at time t₁, the voltage of the minimumcapacity cell becomes equal to or less than the alarm voltage valueV_(a). Therefore, the voltage of the minimum capacity cell is in a statewhere the alarm condition is satisfied.

As shown in FIG. 5, at time t₁, when the alarm condition in which thevoltage of the minimum capacity cell is equal to or less than the alarmvoltage value V_(a) is satisfied (S130; Yes), the battery control unit400 outputs the first signal for reducing the discharge current in thedischarge (S140).

In addition, as shown in FIG. 6(b), at time t₁, the residual capacity ofthe minimum capacity cell is C_(a). That is, the residual capacity ofthe minimum capacity cell is larger than the first value C₁ which is acorrection value. Meanwhile, the residual capacities of all the batterycells 100 are also larger than the first value C₁ which is a correctionvalue.

Next, when the first signal is received from the battery control unit400 after time t₁, the load control unit 640 reduces the dischargecurrent (S150). In this case, the load control unit 640 controls theload 600 so that the estimation value of the residual capacity becomesequal to the first value C₁ when the voltage of the minimum capacitycell becomes the reference voltage V₁, on the basis of the first signal.

That is, as shown in FIG. 6(a), after time t₁, the load control unit 640can perform control so that the voltage of the minimum capacity cell isset to a value larger than the reference voltage V₁ by reducing thedischarge current on the basis of the first signal. After time t₁, thevoltage of the minimum capacity cell drops gently.

In addition, as shown in FIG. 6(b), after time t₁, the current reducesdrastically by controlling the load control unit 640. Thus, the residualcapacity of the minimum capacity cell is reduced gently.

Next, the battery control unit 400 determines whether the voltage of theminimum capacity unit is equal to the reference voltage V₁, and theestimation value of the residual capacity is equal to the first value C₁(S160). When this condition is not satisfied (S160; No), the loadcontrol unit 640 continues the control for reducing the dischargecurrent.

Next, as shown in FIG. 6(a), further, the load control unit 640 controlsthe discharge current, and thus the voltage of the minimum capacity cellbecomes equal to the reference voltage V₁ at time t₃.

In this case, as shown in FIG. 6(b), the residual capacity of theminimum capacity cell becomes equal to the first value C₁ which is acorrection value. In this manner, when the voltage of the minimumcapacity unit becomes equal to the reference voltage V′, and theestimation value of the residual capacity becomes equal to the firstvalue C₁ (S160; Yes), the battery control unit 400 outputs a secondsignal which is different from the first signal (S170).

When the second signal is received, the load control unit 640 fixes thedischarge current to the present current value at time t₃ (S180).Thereby, even after time t₃, the estimation value of the residualcapacity can be made to be equal to a residual capacity expected fromthe voltage of the minimum capacity cell.

As described above, a discharge control according to the secondembodiment is performed.

According to the second embodiment, it is possible to obtain the sameeffect as that in the first embodiment. Further, according to the secondembodiment, when the voltage of the minimum capacity unit becomes equalto the reference voltage V₁, and the estimation value of the residualcapacity becomes equal to the first value C₁, the load control unit 640fixes the discharge current to the present current value. Thereby, fromthe time when the above condition is satisfied, the estimation value ofthe residual capacity can be made to be equal to a residual capacityexpected from the voltage of the minimum capacity cell.

Third Embodiment

FIG. 7 is a schematic diagram illustrating a configuration of anelectronic device 60 according to a third embodiment. The thirdembodiment is the same as the first embodiment, except that there are aplurality of loads 600. Hereinafter, a detailed description will begiven.

Here, as shown in FIG. 7, the electronic device 60 according to thethird embodiment is, for example, a portable communication terminal thatperforms a phone call or packet communication through the transmissionand reception of electromagnetic waves.

This electronic device 60 includes, for example, a sound output unit(sound output unit 601), a display unit 602 provided with alight-emitting unit, an operating unit (operating unit 603), a soundinput unit (sound input unit 604), a communication unit (communicationunit 605), an arithmetic operation process unit (processor unit 606), astorage unit (storage unit 607) and a load control unit (load controlunit 640). The arithmetic operation process unit (processor unit 606) isused for performing an arithmetic operation process of the electronicdevice 60.

The sound output unit 601 is a speaker that outputs a sound of a phonecall. In addition, the sound input unit 604 is a microphone that inputsa sound of a phone call. In addition, the display unit 602 provided witha light-emitting unit is a liquid crystal display device that displayscharacters such as a phone number or a mail, and an image. In addition,the processor unit 606 performs an arithmetic operation process on asignal such as a sound signal of a phone call or data of packetcommunication. The storage unit 607 stores data such as a phone numberor a mail. The communication unit 605 transmits and receives a signalsuch a sound signal or packets through electromagnetic waves. In thismanner, the electronic device 60 of the third embodiment includes aplurality of loads 600.

The load control unit 640 is connected to the same battery pack 10 asthat in the first embodiment, in a region which is not shown in thedrawing. In addition, the load control unit 640 is connected to each ofthe loads 600 mentioned above. Thereby, the load control unit 640 cancontrol the amount of power consumption of each of the loads 600.

Meanwhile, an interconnect (not shown) for supplying power to each ofthe loads 600 may not necessarily be connected to each of the loads 600through the load control unit 640.

Here, a state of S140 in FIG. 2 is assumed. That is, this state is astate where an alarm condition in which the voltage of the minimumcapacity cell in the battery pack 10 is equal to or less than the alarmvoltage value V_(a) is satisfied, and the battery control unit 400transmits the first signal to the load control unit 640.

When all the loads 600 are used as they are, the voltage of the minimumcapacity cell reaches the reference voltage V₁. That is, the estimationvalue of the residual capacity is forcibly corrected to the first valueC₁. Consequently, when the first signal is received from the batterycontrol unit 400, the load control unit 640 reduces the dischargecurrent of the loads 600 as follows.

For example, as is the case with the first embodiment, the load controlunit 640 gradually drops the luminance of the light-emitting unit of thedisplay unit 602. In this manner, the load control unit 640 graduallyreduces the discharge current consumed in the loads 600.

In addition, for example, as is the case with the first embodiment, whenthe first signal is received from the battery control unit 400, the loadcontrol unit 640 may cause the display unit 602 of the electronic device60 to display the start of the control for reducing the dischargecurrent. Thereby, it is possible to prepare a user for the use of theelectronic device 60 being restricted.

In addition, for example, the load control unit 640 lowers theprocessing speed of the processor unit 606. Here, “lowers the processingspeed of the processor unit 606” is to lower the clock frequency of theprocessor unit 606. In this manner, it is possible to reduce a currentconsumed in the processor unit 606 by lowering the clock frequency.

In addition, for example, the load control unit 640 controls thecommunication unit 605 so as to restrict a phone call and perform onlypacket communication. In the transmission and reception of a soundsignal through a phone call, power consumed in the communication unit605 is greater than in the transmission and reception of a data signalthrough packet communication. In this manner, the load control unit 640can impose a restriction of using only the load 600 having relativelysmall power consumption.

As described above, the load control unit 640 may gradually reduce thenumber of loads 600 that consume power at the present time. Thereby, itis possible to reduce the discharge current in units of the loads 600.

According to the third embodiment, the electronic device 60 includes theplurality of loads 600. In such a case, when the first signal isreceived from the battery control unit 400, the load control unit 640can appropriately select a method of reducing a discharge current. Theload control unit 640 may gradually reduce the number of loads 600 thatconsume power at the present time. Thereby, it is possible to reduce thedischarge current in units of the loads 600. Therefore, even when theelectronic device 60 includes a plurality of loads 600, it is possibleto suppress the forcible correction of the estimation value of theresidual capacity. In addition, a user employs the load 600 capable ofbeing used restrictively, but can use the electronic device 60continuously.

Fourth Embodiment

FIG. 8 is a schematic diagram illustrating a configuration of anelectronic device 60 according to a fourth embodiment. The fourthembodiment is the same as the first embodiment, except that theelectronic device 60 is a motive power control device of a hybrid car oran electric automobile. Hereinafter, a detailed description will begiven.

Here, as shown in FIG. 8, the electronic device 60 according to thefourth embodiment is, for example, a motive power control device such asa hybrid car. The same battery pack 10 as that in the first embodimentis mounted to the hybrid car, and is connected to the electronic device60.

This electronic device 60 includes an electric drive unit (motor unit608), a fuel drive unit (engine unit 609), a load control unit (loadcontrol unit 640) and an inverter 660. The load control unit 640 isconnected to the battery control unit 400 of the battery pack 10, in aregion which is not shown in the drawing. In addition, the inverter 660is connected to the external positive electrode terminal 710 and theexternal negative electrode terminal 720 of the battery pack 10, in aregion which is not shown in the drawing. Meanwhile, the electric driveunit (motor unit 608) is used for converting electrical energy intomechanical energy, and the fuel drive unit (engine unit 609) is used forconverting combustion energy of fuel into mechanical energy.

The motor unit 608 converts power from the battery pack 10 into motivepower of an automobile. In addition, the motor unit 608 converts themotive power of an automobile into power through the inverter 660, andcan supply the converted power to the battery pack 10.

The engine unit 609 provides motive power to an automobile by burninggasoline. The load control unit 640 is connected to the motor unit 608and the engine unit 609. Thereby, the load control unit 640 controls aratio by which each of the loads 600 contributes to the motive power ofan automobile.

Meanwhile, an interconnect (not shown) for supplying power to the motorunit 608 may not necessarily be connected through the load control unit640.

Here, the hybrid car is driven by the motor unit 608, and is assumed tobe in a state of S140 in FIG. 2. That is, this state is a state where analarm condition in which the voltage of the minimum capacity cell in thebattery pack 10 is equal to or less than the alarm voltage value V_(a)is satisfied, and the battery control unit 400 transmits the firstsignal to the load control unit 640.

When only the motor unit 608 continues to be driven as it is, thevoltage of the minimum capacity cell reaches the reference voltage V′.That is, the estimation value of the residual capacity is forciblycorrected to the first value C₁. Consequently, when the first signal isreceived from the battery control unit 400, the load control unit 640reduces the discharge current of the loads 600 as follows.

For example, the load control unit 640 reduces the power supply amountfrom the battery pack 10 to the motor unit 608, and increases a driveratio in the engine unit 609. In other words, the load control unit 640performs control so that the contribution ratio to motive power becomesgradually larger in the engine unit 609. Meanwhile, the drive may beswitched from the motor unit 608 to the engine unit 609. Thereby, it ispossible to reduce a discharge current consumed in the motor unit 608.In this manner, it is possible to perform gradual switching to the load600 (engine unit 609) using other energy.

According to the fourth embodiment, it is possible to obtain the sameeffect as that in the first embodiment.

As described above, in the fourth embodiment, a case of the hybrid carhas been described, but an electric automobile may be used. In thiscase, when the first signal is received from the battery control unit400, the load control unit 640 reduces a discharge current by reducingpower which is supplied to the motor unit 608. Meanwhile, in this case,since there is only one motive power source, it is preferable that theload control unit 640 gradually reduce the discharge current.

In addition, in the fourth embodiment, a case of the hybrid car has beendescribed, but an electric power-assisted bicycle may be used. In a caseof an electric power-assisted bicycle, it is considered that an assistforce is lowered in association with the forcible correction of theresidual capacity. In that case, a user feels that the bicycle hasincreased in weight. Consequently, when the first signal is receivedfrom the battery control unit 400, the load control unit 640 graduallyreduces the power which is supplied to the motor unit 608. That is, theload control unit 640 gradually weakens an assist force of the motorunit 608. Thereby, it is possible to use the motor unit 608 with littlechange in load felt by a user.

Fifth Embodiment

FIG. 9 is a schematic diagram illustrating a configuration of anelectronic device 60 according to a fifth embodiment. The fifthembodiment is the same as the first embodiment, except that theelectronic device 60 is connected to at least one or more other powersupply units 12 other than the battery pack 10. Hereinafter, a detaileddescription will be given.

Here, as shown in FIG. 9, the electronic device 60 according to thefifth embodiment is, for example, a power control device that controlspower from a plurality of power supply sources.

The same battery pack 10 as that in the first embodiment is connected toa solar battery 92. The solar battery 92 converts light energy ofsunlight into power. When photovoltaic power is supplied from the solarbattery 92, the battery pack 10 is charged by the power.

In addition, the electronic device 60 includes a converter unit 670 anda load control unit 640. The converter unit 670 converts a directcurrent supplied from the battery pack 10 into an alternating current.In addition, the converter unit 670 has a function of transmitting afirst signal which is transmitted from the battery pack 10. Meanwhile,an interconnect (not shown) for transmitting the first signal from thebattery pack 10 directly to the load control unit 640 may be connectedthereto. In addition, the battery pack 10 is connected to the converterunit 670 of the electronic device 60.

The load control unit 640 is connected to other power supply units 12.The power supply unit 12 is, for example, a distribution switchboard ofpower which is supplied from an electric power company. For example, analternating current is supplied from the power supply unit 12.

The load control unit 640 is connected to a plurality of household powersupply receptacles 610. Various loads 600 are connected to the powersupply receptacles 610 by a user.

Here, it is assumed that power is supplied to the power supplyreceptacles 610 from the battery pack 10. In addition, the battery pack10 is assumed to be in a state of S140 in FIG. 2. That is, this state isa state where an alarm condition in which the voltage of the minimumcapacity cell in the battery pack 10 is equal to or less than the alarmvoltage value V_(a) is satisfied, and the battery control unit 400transmits the first signal to the load control unit 640.

When power is continuously consumed from only the battery pack 10 as itis, the voltage of the minimum capacity cell reaches the referencevoltage V₁. That is, the estimation value of the residual capacity isforcibly corrected to the first value C₁

Consequently, when the first signal is received from the battery controlunit 400, the load control unit 640 reduces the power supply amount fromthe battery pack 10 to the power supply receptacles 610, and increasesthe power supply amount from other power supply units 12 to the powersupply receptacles 610. Thereby, it is possible to suppress the forciblecorrection of the estimation value of the residual capacity to the firstvalue C₁.

Meanwhile, a ratio by which the other power supply units 12 contributemay be gradually increased without discontinuously switching from thebattery pack 10 to other power supply units 12.

According to the fifth embodiment, the electronic device 60 is connectedto at least one or more other power supply units 12 other than thebattery pack 10. In such a case, it is also possible to obtain the sameeffect as that in the first embodiment. In addition, when the batterypack 10 is provided in preparation for the failure of power supply ofother power supply units 12, it is preferable that the battery pack 10be able to be used for a long time. Therefore, according to the fifthembodiment, it is possible to prevent the residual capacity of thebattery pack 10 from being drastically reduced, and to sustain thebattery pack 10 for a long time.

Sixth Embodiment

FIG. 10 is a circuit diagram illustrating a configuration of a batterypack 10 and an electronic device 60 according to a sixth embodiment. Thesixth embodiment is the same as the first embodiment, except that thecontrol circuit 20 of the battery pack 10 in the first embodiment isincluded in the electronic device 60. Hereinafter, a detaileddescription will be given.

As shown in FIG. 10, the battery pack 10 of the sixth embodiment is notprovided with the control circuit 20. That is, the battery pack 10includes only a plurality of battery cells 100 which are connected inseries to each other. The positive electrode terminal 160 is provided onthe side of Cell 1 of the battery pack 10. On the other hand, thenegative electrode terminal 180 is provided on the side of Cell N of thebattery pack 10. In addition, a battery cell terminal 130 is providedbetween each of the battery cells 100.

The electronic device 60 of the sixth embodiment includes themeasurement unit 200, the battery control unit 400 and the switch 500 inaddition to the load 600 and the load control unit 640. A measurementterminal 760 is provided on the battery pack 10 side of the electronicdevice 60.

In addition, a positive electrode terminal 740 and a negative electrodeterminal 750 are provided on the battery pack 10 side of the electronicdevice 60. The positive electrode terminal 740 and the negativeelectrode terminal 750 of the electronic device 60 are respectivelyconnected to the positive electrode terminal 160 and the negativeelectrode terminal 180 of the battery pack 10. Thereby, the electronicdevice 60 can receive a supply of power from the battery pack 10.

In addition, the measurement unit 200 is connected to the measurementterminal 760. The measurement terminal 760 of the electronic device 60is connected to the battery cell terminal 130 of the battery pack 10through an interconnect (no sign shown). Thereby, the measurement unit200 can measure the voltage of each of the battery cells 100.

According to the sixth embodiment, it is possible to obtain the sameeffect as that in the first embodiment. Further, according to the sixthembodiment, it is possible to simplify the battery pack 10 which isfrequently exchanged.

In the aforementioned embodiments, a case has been described in whichthe battery control unit 400 transmits a signal to the switch 500through the measurement unit 200, but the battery control unit 400 maytransmit a signal directly to the switch 500.

As described above, although the embodiments of the present inventionhave been set forth with reference to the drawings, they are merelyillustrative of the present invention, and various configurations otherthan those stated above can be adopted. For example, in the aboveembodiments, a case where the battery cell 100 is a laminate-typebattery has been described, but the effect of the present invention canbe obtained similarly even when the battery cell 100 is a battery havingother forms such as a cylindrical shape and a square shape.

The invention claimed is:
 1. A battery control system comprising: ameasurement unit configured to measure voltages and currents of aplurality of battery units, which are connected in series to each other;a battery control unit configured to control discharge of the batteryunits on the basis of the voltages measured by the measurement unit; anda terminal, which is connected to the battery control unit, configuredto communicate with an external device, wherein the battery control unitis further configured to: specify a minimum capacity unit in which thevoltage is lowest, on the basis of the voltages measured by themeasurement unit, determine an estimation value of a present residualcapacity of the battery units by integrating the currents, continue thedischarge of all the battery units while an alarm condition is notsatisfied, the alarm condition being a condition in which the voltage ofthe minimum capacity unit is equal to or less than an alarm voltagevalue, the alarm voltage value being a voltage value that is greaterthan a reference voltage value that serves as a trigger of a process ofcorrecting the estimation value of the residual capacity, and output afirst signal via the terminal when the voltage of the minimum capacityunit satisfies the alarm condition.
 2. The battery control systemaccording to claim 1, wherein the battery control unit is furtherconfigured to correct the estimation value of the residual capacity to apredetermined first value that is greater than zero when the voltage ofthe minimum capacity unit equals the reference voltage value.
 3. Thebattery control system according to claim 1, wherein the referencevoltage is greater than a discharge termination voltage value at whichthe battery units are over-discharged.
 4. The battery control systemaccording to claim 1, wherein the battery control unit is furtherconfigured to output a residual capacity signal indicating theestimation value of the residual capacity of the battery units.
 5. Thebattery control system according to claim 1, further comprising adisplay unit configured to display the estimation value of the residualcapacity of the battery units.
 6. The battery control system accordingto claim 1, further comprising a load control unit that is connected tothe battery control unit, and the load control unit is configured toreceive the first signal and control a load consuming power of thedischarge, wherein the load control unit is further configured to reducethe discharge current when the first signal is received from the batterycontrol unit.
 7. The battery control system according to claim 6,wherein the battery control unit is further configured to, when thevoltage of the minimum capacity unit becomes equal to the referencevoltage, or the estimation value of the residual capacity becomes equalto the first value, output a second signal, which is different from thefirst signal, and the load control unit is further configured to fix thedischarge current to a present current value when the second signal isreceived.
 8. The battery control system according to claim 1, whereinthe battery units include a lithium-ion secondary battery.
 9. A batterypack comprising: a plurality of battery units which are connected inseries to each other; a measurement unit configured to measure voltagesand currents of the battery units; a battery control unit configured tocontrol discharge of the battery units on the basis of the voltagesmeasured by the measurement unit; and a terminal, which is connected tothe battery control unit, configured to communicate with an externaldevice, wherein the battery control unit is further configured to:specify a minimum capacity unit in which the voltage is lowest, on thebasis of the voltages measured by the measurement unit, determine anestimation value of a present residual capacity of the battery units byintegrating the currents, continue the discharge of all the batteryunits while an alarm condition is not satisfied, the alarm conditionbeing a condition in which the voltage of the minimum capacity unit isequal to or less than an alarm voltage value, the alarm voltage valuebeing a voltage value greater than a reference voltage value that servesas a trigger of a process of correcting the estimation value of theresidual capacity, and output a first signal, via the terminal, when thevoltage of the minimum capacity unit satisfies the alarm condition.